Infrared transmitting glass



Feb. 25, 1947.l

H. P. HOOD INFRARED TRANSMITTING GLAS S Filed June4 17. 1944 inhentutSEMS Patented Feb. 25, 1947 .Harrison P. Hood, Corning,- N. Y., assignorlto Corning Glass Works, Corning' N. Y., a corporation of New YorkApplication June 17, 1944, Serial No. 540,792

5 Claims. (o1. 10c-52p) This invention relatesy to glasses which areopaque to Avisible radiations but substantially transparent to infraredradiations. A The primary object of the invention is to pro vide a glasswhich has a specie infrared transmission'rendering it particularlysuitable for various purposes.

Another Objectis to provide a glass which is suitable for use as a lightfilter in conjunction with photoelectric cells which are sensitive to ispecific infrared radiations.

Another object is' to provide a glass which is suitable for use vas alter in infrared therapy.

Another. object is to provide `a glass which transmits Wave lengths'between- .7 `and 1.1# (micron) but which'absorbs the remainder of theinfrared and the visible spectrum.

Prior glasses for transmitting the infrared and absorbing the visiblespectrum were colored with a substantial amount of manganese, as isshown in Taylor Patent 1,411,133. Such glasses have a relatively hightransmission for wave lengths longer than la but considerably lesstransmission for infrared wave lengths less than 1.a.

vFor some purposes a selective tr-ansmission of the shorter infraredwave lengths is desirable.

For example, in the therapeutic use of infrared radiations a glass isneeded which has a high transmission for the skin-penetrating wavelengths in the region .7 to 1.2M and complete ab sorption of theinjurious longer wave lengths which cause blistering. Absorption of Ywave lengths shorter than .7a is also desirable although their completeexclusion is not essential for this purpose. r

Glasses having the same spectral transmission characteristics are alsoneeded for use inV apparatus, such as burglar alarms, signalling devicesand the like, embodying a photoelectric cell, such as the so-calledcaesium cell, which has a maximum infrared sensitivity approximatelycentered between .8 and .9a. For` this purpose the complete absorptionof visible radiations is highly desirable.

I have discovered that the above described selenium and cadmium sulfidewill develop aruby i yZ color maybe `employed as the base composition ofmy new glasses. In' general, the presence of zinc oxideis essential andany silicate glass which *con-A tains at .1Q2ist- 2% or more ofv zincoxide will de-j velop. a ruby color `with selenium and cadmium sulde.Other non-coloring oxides such as alumi-A na, boric oxide, oxides of theother metals of the second periodic group, etc., may be present if theydo not prevent the development of color by the selenium. When othersecond group metal oxides are present, the ypercentage of zinc oxideshould preferably be increased. Glasseswhich are free from zinc,particularly if melted reducingly,"lack the high transmission between .7and 1.1;, which is characteristic of my new glasses. If desired', 10Wexpansion glassesf embodying my invention maybe produced without`depreciationin spec'- tral characteristics by introducing boric oxideinto the glass and lowering the alkali content in the manner known formaking low expansion glasses. The coloring materials should preferablybe present in the following proportions:

Either a cobaltic or a cobaltous compound may be used in the batch, butthe latter is preferable because the former has an oxidizing effect.When a higher oxide of a polyvalent metal, say C0203, is present in thebatch, some of the cadmium suliide used as'a coloring agent may beoxidized to cadmium oxide and some of the selenium may be lost. Undersuch conditions the full color of the glass may not develop and itsabsorption of 'visible light may be incomplete unless the glass isreheated to warm in the desired coloration. The presence of strongoxidizing agents should be avoided, but minor oxidizing effects may becompensated by increasing the proportions of cadmium' sulfide andselenium and/or by adding to the batch a small amount of a reducingagent suiiicient only to neutralize the objectionable oxidizing effects.l'. have found that ammonium chloride is particularly suitable becauseit acts as a Very mild reducing agent in such glasses and permits a veryaccurate control of the optimum degree of reduction.

As examples illustrating my invention, the foll lowing compositions aregiven in weight percentage as calculated from their respective batches:

Referring to the drawing, the full line curve A represents the percenttransmission in'v 3 mm.

1 thickness of glass No. 1 of the above table when.

made with C0203 and subsequently warmed in.

The dotted line curve B represents the small visible transmission whichthe same glass possesses before warming in. The dashed line curve C 3represents the transmission in 2.5 mm. thickness of apriorinfrared-transmitting,manganese-containing glass made in accordancewiththe Taylor Patent 1,411,133` It will be observed that the priorglass, although it completely absorbs rthe visible, has: a substantialtransmission throughout the infrared to about 4a. The new glasstransmits little,

if any, of the infrared outside of the region betweenV .7 and 1.111, thetransmission for the given thickness in this region rising to a maximumof over 80% with a very sharp cut-oli.

I claim: 1. An infrared transmitting glass which conzinc oxide andcoloring materials consisting of l .7% to 2% selenium, 1.% to .3%cadmium sulfide,

and2%to 3% cobalt oxide, as calculated from its f batch, and which in athicknesslof 2 to'3 mm. has

i tains silica, alkali metal oxide, at least 2% of a high transmissionfor wave lengths from .'75 to 1p., but substantially no transmission forthe remainder of the infrared nor the visible spectrum.

2. An infrared transmitting glass which contains silaca, alkali metaloxide, at least 2% of zinc oxide and coloring materials consisting of.7-2% Se, 1-3% CdS, and 2-3%'CoO, as calculated from its batch, andwhich in a thickness of 2 to 3 mm. has a high transmission for wavelengths from .75 to 1u, but substantially no transmission for theremainder of the infrared.

3. An infrared transmitting ,glass which contains approximately 58%SiOz, 17.5% KzO, 7% ZnO, 13% BaO, .7% Se, 1% CdS, and 2.5% COO,

as calculated from its batch.

'4. An infrared transmitting glass which contains silica, alkali metaloxide, at least 2% of zinc oxide and coloring materials consisting ofSe, CdS and CoO, .the glass having a spectral transmissionband betweenWave lengths .7u and 1.1/1., while substantially completely absorbingwave lengths longer than 1.17.

5. An infrared transmitting glass which contains silica, alkali metaloxide, at least 2% of zinc oXide and coloring materials consisting ofnot over 2% Se, not over 3% CdS and not over 3% CoO, the glass having 'aspectral transmission band between-wave lengths .7 /t-and 1.111, whilesubstantially completely absorbing Wave lengths longer than 1.111. l

' HARRISON P. HOOD.

REFERENCES CITED The following references are of record in the le oi"this patent:

UNITED STATES PATENTS Rising Aug. 29, 1933V

